Prairie! What does this word remind you of? Perhaps a television program, an old movie, or the series of books by Laura Ingalls Wilder. The word “prairie” is from the French word for a meadow grazed by cattle. It was applied by the early French explorers to the vast inland area of North America that is mostly devoid of trees and instead covered with waving grasses and a vast variety of colorful wildflowers in various shades of yellow, white, pink, and blue. It is an unforgettable experience to be out on a prairie on a beautiful day when dozens of different kinds of plants are in bloom, insects are busily pollinating the flowers, birds are singing, and a brisk wind is blowing.

“The Prairie State” is a frequently used nickname for Illinois, yet few people know what a prairie is or have ever visited one. At the same time, there is a growing awareness of prairies. Prairies are an important part of this state’s heritage, and in the past few years there have been numerous conferences, radio programs, popular articles, books and scientific papers on prairies. Unfortunately, most of this information is not readily available. This website provides an introduction to the fascinating world of prairies.

What is a prairie?

map of prairie region, in green, in the central and western U.S.

Prairies are a type of grassland, a landscape dominated by herbaceous plants, especially grasses; trees are either absent or only widely scattered on the landscape. Grasslands occur in many regions, such as the llanos of Venezuela, the pampas of Argentina, the cerrado and campos of Brazil, the steppes of central Asia, the veldt and savannas of Africa, and the grasslands of Australia. Approximately 32 to 40% of the world’s land surface is, or was, covered by grasslands. Today, grasslands are extremely important for agriculture, and approximately 70% of the food produced for humans comes from these regions.

Grasslands are the largest vegetation type in North America, covering approximately 15% of the land area. Prairies are the grasslands found in the central part of the North American continent. They form a more or less continuous, roughly triangular area that extends for about 2,400 miles (3,870 km) from Alberta, Saskatchewan, and Manitoba southward through the Great Plains to southern Texas and adjacent Mexico and approximately 1,000 miles (1,612 km) from western Indiana westward to the foothills of the Rocky Mountains, covering 1.4 million square miles. Rainfall decreases from east to west, resulting in different types of prairies, with the tallgrass prairie in the wetter eastern region, mixed-grass prairie in the central Great Plains, and shortgrass prairie towards the rain shadow of the Rockies. Today, these three prairie types largely correspond to the corn/soybean area, the wheat belt, and the western rangelands, respectively.

Illinois lies within an area called the “prairie peninsula,” an eastward extension of prairies that borders deciduous forests to the north, east, and south. This is part of the tallgrass prairie region, sometimes called the true prairie, with the landscape dominated by grasses such as big bluestem and Indian grass as well as a large number of other species of grasses and wildflowers, the latter called forbs. The vegetation sometimes reaches a height of 10 feet or more.

The first European settlers moving westward from the forests of the eastern United States encountered the prairies, which seemed like a vast ocean of grass. The wind caused waves on the surface of the shimmering grasses. One type of wagon used by the pioneers was the “prairie schooner,” a reference to a sailing vessel, further adding to the analogy of the prairie being a large inland sea of grasses. It was easy to get lost in the prairie, especially since there were few trees or other natural features to act as landmarks. Even when on horseback, it was often not possible to see across the prairie to the horizon.

Formation of Prairies

Prairies are one of the most recently developed ecosystems in North America, formed after the period of Pleistocene glaciation. About 18,000 years ago, much of Illinois was covered by glaciers. As the glaciers melted, the land was covered at first with tundra type vegetation, then by spruce forests. As the climate became warmer and drier, between 14,000 and 10,000 years ago, a cool mesic hardwood forest with ash, oak, elm, maple, birch, and hickory trees replaced the spruce forest. About 8,300 years ago, the climate became substantially warmer and drier, and within the relatively short time of 500 to 800 years, most of the forests in Illinois died out, except along stream banks, and prairies spread over the landscape. For more information about glaciation in North America, see the excellent book by E. C. Pielou, After the Ice Age (1991).

During the last 1,000 years the climate has become slightly cooler and wetter, making conditions more favorable to trees. Savannas, characterized by a grassy prairie-type ground cover underneath an open tree canopy, were common in northeastern Illinois. Scattered out on the prairie were patches of rich forests completely surrounded by prairie; these forests are called prairie groves.

Prairies developed and were maintained under the influence of three major non-biological stresses: climate, grazing, and fire. Occurring in the central part of North America, prairies are subject to extreme ranges of temperatures, with hot summers and cold winters. There are also great fluctuations of temperatures within growing seasons.

Rainfall varies from year to year and within growing seasons as well. The prairie region is also subject to droughts. Usually there is a prolonged dry period during the summer months, and in addition there are major droughts lasting for several years that occur every 30 years or so. People are often surprised to hear that the annual rainfall in Champaign, Illinois is seven inches MORE per year than London, England (35″ vs. 28″), but London rarely has the kind of severe droughts found in central Illinois or the prairie region in general.

Before European settlement, the eastern boundary of the prairie was in a state of flux. During periods of drought, trees died and prairie plants took over previously forested regions. When rainfall was abundant, the trees and forest were able to reestablish themselves.


Prairie fires, started either by lightning or by Native Americans, were commonplace before European settlement. Any given parcel of land probably burned once every one to five years. These prairie fires moved rapidly across the prairie, and damaging heat from the fire did not penetrate the soil to any great extent. Fire kills most saplings of woody species, removes thatch that aids nutrient cycling, and promotes early flowering spring species. Today fire also is beneficial to control non-native herbaceous species that can invade prairie remnants.

A considerable portion of the above ground biomass of a prairie was consumed each year by the grazing of a wide range of browsing animals, such as bison, elk, deer, rabbits, and grasshoppers. This grazing was an integral part of the prairie ecosystem, and therefore grasslands and ungulate mammals coevolved together. Grazing increased growth in prairies, recycles nitrogen through urine and feces, and the trampling opens up habitat for plant species that prefer some disturbance of the soil.

Prairie plants have adapted to these stresses by largely being herbaceous perennials with underground storage/perennating structures, growing points slightly below ground level, and extensive, deep root systems. The tender growing points of prairie plants occur an inch or so below ground and are usually not injured by prairie fires, which move rapidly across the prairie. These underground growing points are also left unharmed by browsing animals. During droughts, the deep roots of prairie plants are able to take up moisture from deep in the soil.

European Settlement

When European settlers began moving westward from the original eastern States, they encountered large expanses devoid of trees but covered with a sea of tall grasses and wildflowers undulating in the wind. The settlers adopted the French word ‘prairie.’

The early settlers, originally from the forested regions of Europe, found the prairies to be rather frightening. They were not used to the hordes of biting insect, intense summer heat and high humidity, bleak, windy winters, and periodic raging prairie fires. Because no trees grew on the prairie, the settlers at first considered the prairies to be infertile. This, plus the need for firewood and construction timber prompted them to build homes at the edges of the prairies and along rivers, where trees persisted. It was not long, however, before the settlers discovered that the prairie soil was more fertile than forest soil, and was in fact among the most productive soils in the world.

conestoga wagon illustration

The settlers often came by way of prairie schooner. The prairie was sometimes called a “sea of grass,” and schooners are small, sea-going sailing ships. Prairie schooners were also called covered wagons or conestogas.

A difficulty the settlers encountered was that their plows, made for forest soils, were not able to cut through the dense prairie sod. It was not until 1837, when John Deere invented the self-scouring, steel-bladed plow in Grand Detour, Illinois, that it was possible to break the prairie sod and farm the prairie on a large scale. Then, in a remarkably short period of perhaps 50 years, the vast majority of prairie in Illinois was plowed and converted to agriculture. Prior to settlement, more than 60% of Illinois, approximately 22 million acres, were covered with prairie. Today, just over 2,000 acres remain, less than one-hundredth of one percent.

Types of Prairies in Illinois

The natural landscape of Illinois can be divided into 14 natural divisions, based on topography, glacial history, bedrock, soils, and distribution of plants and animals. The prairies of Illinois were by no means a homogeneous stand of grasses and forbs, and the comprehensive natural community classification1 adopted for Illinois includes six main subclasses of prairie:

Further divisions are made based on soil moisture classes, yielding 23 prairie types in Illinois.

The largest original prairie type was the Grand Prairie (black soil prairie) of central Illinois, with flat landscapes, deep loess soil, and poor natural drainage resulting in wet conditions during part of the year. This kind of prairie is the rarest today because the soil is so productive for agricultural crops.

Along the shores of Lake Michigan and the Illinois, Kankakee, and Mississippi rivers, are extensive sand deposits, often forming dunes or ridges and swales, and several kinds of sand prairies can be found in such areas.

Hill prairies are found on dry, southwest-facing, loess-covered hill tops above bluffs overlooking floodplains of rivers, especially the Illinois and Mississippi rivers.

In northeastern Illinois some distinctive prairie vegetation can be found in very wet alkaline fens and marl flats.

pink echinaceaBiodiversity in Prairies

According to a document produced by The Nature Conservancy, the tallgrass prairie is “the most diverse repository of species in the Midwest [and] … habitat for some of the Midwest’s rarest species.”

It is rather difficult to give a total number of species that occur on prairies in Illinois. Since the tallgrass prairie ecosystem is recently evolved, there are few endemic species and few species that occur on prairies are restricted to the prairie habitat. Most prairie species also occur outside the prairie region in habitats other than prairies.

Prior to European settlement, the landscape of the tallgrass prairie in Illinois was a complex matrix with specialized communities embedded in the prairie:

  • fens,
  • pannes,
  • sedge meadows,
  • marshes,
  • ponds,
  • kames,
  • sand blowouts,
  • savannas, and
  • prairie groves.

The borders between these communities and the prairie fluctuated on both short and long term bases depending on rainfall, drought, and fire frequency. This ever changing matrix adds to the problem of placing some species into the “prairie species” category. For this discussion we include all species that occupy or utilize during some stage of their life cycle the types of habitats recognized as prairie by the Illinois Natural Areas Inventory; excluded are species restricted to open grass, sedge, and forb-dominated communities classified as wetlands, such as sedge meadows and fens.

The soil underneath the prairie is a dense tangle of roots, rhizomes, bulbs, corms, and rootstocks. While the above ground part of most prairie plants die back each year; the plants are kept alive from year to year by these underground structures. The roots of prairie plants often extend deeper into the ground than the stems rise above it. For instance, the roots of big bluestem may be 7 feet or more deep, and switchgrass roots more than 11 feet deep. Some of the roots die and decompose each year, and this process has added large quantities of organic matter to the soil. This is one reason why the prairie soils are so fertile.


Ken Robertson
Ken Robertson

This website is the work of Dr. Ken Robertson. Thanks to Scott C. McKay, Amanda S. Robertson, Charles Warwick, and Jennifer Tate for proofreading and editorial advice. Karen Fletcher first suggested this article, and she digitized the first slides and did the original html programming for the PrairieNet version of this website.

Some of the information in this article came from work done as part of the Critical Trends Assessment Program. The Critical Trends prairie chapter was prepared by Kenneth R. Robertson and Mark W. Schwartz, with the assistance of Brian K. Dunphy, H. David Clarke, Jeffrey W. Olson, and Lyle Trumbull.

1 J. White and M. H. Madany. 1978. Classification of natural communities in Illinois. Pages 310-405 (Appendix 30) in J. White, Illinois Natural Areas Inventory Technical Report. Volume 1: Survey Methods and Results. Illinois Natural Areas Inventory, Department of Landscape Architecture, University of Illinois at Urbana/Champaign